This post is a few years old, but interesting nonetheless. Art Direction, Props and Authenticity talks about the importance of realism in prop making, specifically the realism of a prop’s weight. A prop that appears too light can take the audience out of the moment.
Game of Thrones has a new video out showing some of the work that goes into their props. It features prop master Gordon Fitzgerald, some drawings of props, and a look at how the smallest details are taken care of.
The Make Magazine blog featured a cool tip for using polycaprolactone plastic to make sanding blocks (they use Shapelock, though Friendly Plastic is another familiar brand name). If you need your sanding block to have a different shape for fitting around a curve or other odd surface, just heat it up in boiling water and reshape it to what you need.
Finally, if you have the time (about a half an hour), here is a good video featuring Adam Savage as he weathers and ages a prop. He articulates his process rather well, even though a lot of the process is carried out by instinct and intuition: